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Construction of the Vlakfontein Reservoir in Gauteng, Benoni is complete. The 210 Ml circular reinforced concrete reservoir is the largest reservoir structure designed by Bosch Projects to date and is likely to be one of the largest post-tensioned concrete reservoirs in the world.

This concrete reservoir, which was awarded for Construction in 2020 by Rand Water, was a joint venture between WBHO Construction, ANZI Plant and Mining Services and the Motheo Construction Group. Construction administration and monitoring was undertaken by Rand Water in collaboration with the Bosch Projects team.  Bosch Projects was included in the design team and the Approved Professional Person (APP) in terms of the Dam Safety Legislation. The size of the reservoir is so large that it has been classified as a dam with a significant hazard rating, which required stringent monitoring by the APP during the construction phase.

The purpose of the project was to provide additional balancing and emergency storage to Rand Water’s domestic and industrial bulk water supply system, supplying the eastern areas of Johannesburg and Ekurhuleni. This system has been under severe strain over the last few years due to increased demand from urban expansion in the eastern areas.

The design team conducted extensive research into possible innovative concepts, of which one was a circular reservoir. Through research and discussions on constructability and the economics of construction, it was decided that a circular post-tensioned reservoir was the preferred option.

In attempt to limit leakage, the reservoir has been designed to have one sliding joint between the reservoir floor slab and the wall footing to take-up thermal and dynamic movements of the reservoir as it fills and empties. A high level of research and detail has gone into to providing adequate water proofing membranes to withstand anticipated movement in this joint.

The reservoir, stores 213.4 million litres of potable water, is circular in shape, with post-tensioned outer concrete walls that are 11.8 m high, similar to a three-storey building. These walls are tapered from a thickness of 1 100 mm at the bottom to 300 mm at the top. The reservoir also boasts an internal diameter of 154 m – the length of one and half football fields – with 256 circular reinforced concrete columns, 600 mm diameter, to support the roof slab.

Well done to the team on another successful project.